|From||"Roger Brugge" <email@example.com>|
|Date||Thu, 16 Jan 2014 09:17:03 +0000|
Forwarded from CLIMLIST... The laboratory of excellence L-IPSL <http://labex.ipsl.fr/90-liens-rapides/95-offres-demplois> of the Institut Pierre-Simon Laplace offers a 2-year post-doctoralposition to work on climate change modeling over West Africa. Context: The Sahel has undergone a severe (large scale and long-lasting) drought in the 1970s-1980s. West Africa has also undergone a strong paleo variability, with evidence for a “green Sahara” about 6000-7000 years ago. The recent Sahelian drought was probably in large part driven by the decadal variations of the sea surface temperature. For people of that region who crucially rely on the monsoon rainfall, anticipating the possible future variations of the African monsoon system is of great importance. However, coupled ocean-atmosphere climate model still show a rather poor skill in simulating the African monsoon, and there is still a large spread of climate projections on that region. The downscaling experiments performed under the Cordex program (which did prioritize the African continent), are at least as dispersed and biased as those from the global models. Despite the important dispersion, CMIP5 models suggest a general tendency to a reinforcement of rainfall in central Sahel, with a slight drying on the Senegal/Guinea coast. This signal may be related to some robust features found in idealized simulation that show that CO2 increase produce a rapid reinforcement of ascending motions in the tropics. This effect could be reinforced by a regional water vapor positive feedback: increased convergence over the Saharan heat low brings more water which in turns strengthens regionally the greenhouse effect. This mechanism share similarities with the response of monsoon to enhanced Northern hemisphere seasonal insulation that prevail during the “green Sahara” period. The general purpose of the work would be twofold: 1) identify the elements of robustness in climate simulations (paleo, historical reconstructions and climate change projections), analyzing the contribution of for instance change in large scale circulation and SSTs, direct CO2 forcing or regional water feedback, and 2) question the strategies for downscaling experiments over West Africa as to their ability to account for the identified critical mechanisms. Description of work: The work will be based in part on the multi-model analysis of CMIP5 simulations (in order to identify robust mechanisms and features), benefiting from the fact that the same model has been used for past climate, historical simulations and climate change projections. A particular focus will be put on the analysis of the radiative forcing (CO2 and aerosols) and feedback (water vapor) over the Saharan heat low. To test physical hypotheses about the role of these forcings and feedbacks on climate change over West Africa, the analysis of existing simulations will be complemented by dedicated simulations with the LMDZ atmospheric general circulation model, which is the atmospheric component of the IPSL Coupled Model (involved in CMIP5). The model can be run either in global mode or zoomed over a particular region of the globe. It can be run either in climatic mode or “nudged” toward the large scale dynamics of the reanalysis or the results of another simulation. The LMDZ physical package has also been coupled to the dynamics of the WRF regional model, which will allow to test the use of limited area model without modifying the physics. This suite of configuration will be used 1) to separate local feedbacks from large scale couplings (using nudging or not at the boundary of the domain, or imposing idealized diabatic heating like albedo patches over a region, or more or less interactions with surface), and 2) to perform big-brother experiments to compare and assess the strengths and limitations of different downscaling approaches: a reference simulation run with a fine global regular grid is used as a reference (or model truth) for various approaches (zoom with or without nudging, limited area versions). Supervision team:The work will be conducted under the main supervision of Frédéric Hourdin from Laboratoire de Météorologie Dynamique <http://www.lmd.jussieu.fr> and Sophie Bastin from Laboratoire Atmosphères, Milieux, Observations Spatiales <http://www.latmos.ipsl.fr/> together with colleagues from the two teams (Cyrille Flamant, Sandrine Bony, Jean-Louis Dufresne....). The work will be performed in alternance between the two labs with a schedule to be discussed, and followed jointly by a larger Labex team who will also imply P. Braconnot (LSCE <http://www.lsce.ipsl.fr>)... Experience: The applicant will have experience with numerical modeling of the Earth system based on global or regional model. He/she also have experience with handling large datasets. The applicant publication record should show a majority of papers published in English in top ranking journals. Duration and salary: The post-doctorate will be recruited for 24 months with a net monthly salary around 2000 euros, commensurate with experience. This includes social services and health insurance. Contact for applications:Applications should include a CV, a statement of research interestsand the names of at least two references including e-mail addresses and telephone numbers. Applications should be submitted by e-mail to Cyrille Flamant (firstname.lastname@example.org <mailto:email@example.com>) before 15 March 2014.
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